Unusual Expansion Research Articles

Observation of the Sixth Polymorph of BiB3O6: In Situ High-Pressure Raman Spectroscopy and Synchrotron X-ray Diffraction Studies on the β-Polymorph

β-BiB3O6 was compressed in a diamond anvil cell at room temperature and studied using a combinstion of in situ high-pressure Raman scattering and angle-dispersive synchrotron X-ray diffraction. The results reveal that β-BiB3O6 retains its structure below 9.0 GPa and undergoes a structural phase transition that starts at ~11.5 GPa and finishes at ~18.5 GPa. No other phase transition occurred with increasing pressure up to ~46 GPa. It was also found that the high-pressure phase is different from the already-reported five polymorphs of BiB3O6. Therefore, the new phase is denoted as ζ-BiB3O6, which could be indexed by an orthorhombic unit cell (a ≈ 12.5 Å, b ≈ 6.7 Å, c ≈ 4.0 Å) from the powder XRD pattern collected at 22.2 GPa. Moreover, ζ-BiB3O6 can be quenched to ambient conditions. The investigation of the pressure dependence of the lattice parameters reveals that both β-BiB3O6 and ζ-BiB3O6 exhibit a large amount of crystallographic anisotropy. An unusual expansion of the c-axis of ζ-BiB3O6 was observed. Assignments for the Raman spectra of β-BiB3O6, γ-BiB3O6, and δ-BiB3O6 under ambient conditions were also performed. Currently, we cannot solve the crystal structure of ζ-BiB3O6 but give some speculations based on its relationship with β-BiB3O6.

Designing Microstructural Architectures With Thermally Actuated Properties Using Freedom, Actuation, and Constraint Topologies

In this paper, we demonstrate how the principles of the freedom, actuation, and constraint topologies (FACT) approach may be applied to the synthesis, analysis, and optimization of microstructural architectures that possess extreme or unusual thermal expansion properties (e.g., zero or large negative-thermal expansion coefficients). FACT provides designers with a comprehensive library of geometric shapes, which may be used to visualize the regions wherein various microstructural elements can be placed for achieving desired bulk material properties. In this way, designers can rapidly consider and compare a multiplicity of microstructural concepts that satisfy the desired design requirements before selecting the final concept. A complementary analytical tool is also provided to help designers rapidly calculate and optimize the desired thermal properties of the microstructural concepts that are generated using FACT. As a case study, this tool is used to calculate the negative-thermal expansion coefficient of a microstructural architecture synthesized using FACT. The result of this calculation is verified using a finite element analysis (FEA) package called ale3d.

Thermal study of the interplay between spin and lattice in CoCr2O4and CdCr2O4

The interplay between spin and lattice degrees of freedom in the spinels CoCr${}_{2}$O${}_{4}$ and CdCr${}_{2}$O${}_{4}$ has been investigated by heat capacity and thermal expansion measurements. In CoCr${}_{2}$O${}_{4}$, sharp anomalies are observed at the magnetic phase transition temperatures of 13, 26, and 93 K. A large pressure dependence of the transition temperature at 13 K, which is calculated from the heat capacity and thermal expansion, indicates strong spin-lattice coupling in the incommensurate phase. This result provides the possibility of the reduction of lattice symmetry from cubic at the phase transition. In CdCr${}_{2}$O${}_{4}$, negative thermal expansion due to spin-lattice coupling emerges in temperature from 140 to 45 K, which is followed by strong positive thermal expansion at lower temperature. The magnetostructural transition at 7.8 K is observed as a large anomaly with an indication for a large pressure dependence of the transition temperature. The unusual thermal expansion suggests the importance of other perturbations besides exchange interactions between Cr ions for the formation of the spin clusters. Our results demonstrate that thermal measurements can help to further understand the frustrated systems with strong spin-lattice coupling.

Selective gas adsorption and unique phase transition properties in a stable magnesium metal-organic framework constructed from infinite metal chains

A 3D Magnesium MOF PCN-72 has been synthesized from the solvothermal reaction of Mg(NO3)2 and a linear ligand. This MOF has a unique structure with 1-dimensional (1D) channel as well as infinite metal chains, which resembles the topology of MIL-53. It is thermally and moisture stable. In situ powder X-ray diffraction studies reveal its interesting phase transitions under temperature change. Calculation shows that each phase of PCN-72 exhibits unique and unusual thermal expansion properties. After removing coordinated solvent at Mg chains, PCN-72 can selectively adsorb CO2 over N2.

Insight into Structure‐Dependent Self‐Activation Mechanism in a Confined Nanospace of Core–Shell Nanocomposites

An unusual hollow core expansion through in situ self-activation in a confined nanospace is observed, which is due to the different physical and chemical properties of the core and shell. The in situ generated gas molecules (e.g., CO2, H2O) preferentially assemble in the hollow core and create immense pressure, which can gasify the formed carbon shells, resulting in substantially increased porosity and a hollow cavity. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Evolutionary study of duplications of the miRNA machinery in aphids associated with striking rate acceleration and changes in expression profiles

BackgroundThe sequencing of the genome of the pea aphid Acyrthosiphon pisum revealed an unusual expansion of the miRNA machinery, with two argonaute-1, two dicer-1 and four pasha gene copies. In this report, we have undertaken a deeper evolutionary analysis of the phylogenetic timing of these gene duplications and of the associated selective pressures by sequencing the two copies of ago-1 and dcr-1 in different aphid species of the subfamily Aphidinae. We have also carried out an analysis of the expression of both copies of ago-1 and dcr-1 by semi-quantitative PCR in different morphs of the pea aphid life cycle.ResultsThe analysis has shown that the duplication of ago-1 occurred in an ancestor of the subfamily Aphidinae while the duplication of dcr-1 appears to be more recent. Besides, it has confirmed a pattern of one conserved copy and one accelerated copy for both genes, and has revealed the action of positive selection on several regions of the fast-evolving ago-1b. On the other hand, the semi-quantitative PCR experiments have revealed a differential expression of these genes between the morphs of the parthenogenetic and the sexual phases of Acyrthosiphon pisum.ConclusionsThe discovery of these gene duplications in the miRNA machinery of aphids opens new perspectives of research about the regulation of gene expression in these insects. Accelerated evolution, positive selection and differential expression affecting some of the copies of these genes suggests the possibility of a neofunctionalization of these duplicates, which might play a role in the display of the striking phenotypic plasticity of aphids.

Uniaxial Negative Thermal Expansion in an Organic Complex Caused by Sliding of Layers

Generally, materials undergo thermal expansion along all directions upon heating. The very few materials that show the opposite trend along one or more of their crystallographic axes have plenty of applications. Herein we report a negative thermal expansion along one axis in the crystal structure of a 1:1:1 organic complex of 1,3,5-benzenetricarboxylic acid (BTA), 2,6-dimethylaniline (DMA), and water molecules. The unusual thermal expansion in this structure is caused by sliding of layers, which is unprecedented.

Neutron diffraction study and anomalous negative thermal expansion in nonsuperconducting PrFe1−xRuxAsO

Neutron powder diffraction has been used to investigate the structural and magnetic behavior of the isoelectronically doped Fe pnictide material PrFe${}_{1\ensuremath{-}x}$Ru${}_{x}$AsO. Substitution of Ru for Fe suppresses the structural and magnetic phase transitions that occur in the undoped compound PrFeAsO. Contrary to the behavior usually observed in 1111 pnictide materials, the suppression of both the structural and magnetic transitions does not result in the emergence of superconductivity or any other new ground state. Interestingly, PrFeAsO itself shows an unusual negative thermal expansion (NTE) along the $c$ axis, from 60 K down to at least 4 K; this does not occur in superconducting samples such as those formed by doping with fluorine on the oxygen site. We find that NTE is present for all concentrations of PrFe${}_{1\ensuremath{-}x}$Ru${}_{x}$AsO with $x$ ranging from 0.05 to 0.75. These results suggest that the absence of superconductivity in these materials could be related to the presence of NTE.

Atomistic Modeling of the Negative Thermal Expansion in δ- Plutonium Based on the Two-State Description.

The δ phase of plutonium with the fcc structure exhibits an unusual negative thermal expansion (NTE) over its narrow temperature range of stability, 593–736 K. An accurate description of the anomalous high-temperature volume effect of plutonium goes beyond the current capability of electronic-structure calculations. We propose an atomistic scheme to model the thermodynamic properties of δ-Pu based on the two-state model of Weiss for the Invar alloys, inspired by the simple free-energy analysis previously conducted by Lawson et al. The two-state mechanism is incorporated into the atomistic description of a many-body interacting system. Two modified embedded atom method potentials are employed to represent the binding energies of two competing electronic states in δ-Pu. We demonstrate how the NTE takes place in δ-Pu by means of Monte Carlo simulations implemented with the two-state mechanism.

Chronic Hepatitis C Virus Infection Breaks Tolerance and Drives Polyclonal Expansion of Autoreactive B Cells

Chronic Hepatitis C virus (HCV) infection has been linked with B cell lymphoproliferative disorders and several autoimmune-related diseases. The mechanisms of how chronic viral infection affects B cell development and predisposes the patients to autoimmune manifestations are poorly understood. In this study, we established an experimental system to probe the B cell responses and characterize the antibodies from chronic-HCV-infected individuals. We identified an unusual polyclonal expansion of the IgM memory B cell subset in some patients. This B cell subset is known to be tightly regulated, and autoreactive cells are eliminated by tolerance mechanisms. Genetic analysis of the immunoglobulin (Ig) heavy chain variable gene (V(H)) sequences of the expanded cell population showed that the levels of somatic hypermutation (SHM) correlate with the extent of cell expansion in the patients and that the V(H) genes exhibit signs of antigen-mediated selection. Functional analysis of the cloned B cell receptors demonstrated autoreactivity in some of the expanded IgM memory B cells in the patients which is not found in healthy donors. In summary, this study demonstrated that, in some patients, chronic HCV infection disrupts the tolerance mechanism that normally deletes autoreactive B cells, therefore increasing the risk of developing autoimmune antibodies. Long-term follow-up of this expanded B cell subset within the infected individuals will help determine whether these cells are predictors of more-serious clinical manifestations.

Psi-series method for equality of random trees and quadratic convolution recurrences

An unusual and surprising expansion of the form as , is derived for the probability pn that two randomly chosen binary search trees are identical (in shape, hence in labels of all corresponding nodes). A quantity arising in the analysis of phylogenetic trees is also proved to have a similar asymptotic expansion. Our method of proof is new in the literature of discrete probability and the analysis of algorithms, and it is based on the logarithmic psi-series expansions for nonlinear differential equations. Such an approach is very general and applicable to many other problems involving nonlinear differential equations; many examples are discussed in this article and several attractive phenomena are discovered.Copyright © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 44, 67–108, 2014

High-Pressure Investigation of Li2MnSiO4 and Li2CoSiO4 Electrode Materials for Lithium-Ion Batteries

In this work, the high-pressure behavior of Pmn2(1)-Li(2)MnSiO(4) and Pbn2(1)-Li(2)CoSiO(4) is followed by in situ X-ray diffraction at room temperature. Bulk moduli are 81 and 95 GPa for Pmn2(1)-Li(2)MnSiO(4) and Pbn2(1)-Li(2)CoSiO(4), respectively. Regardless of the moderate values of the bulk moduli, there is no evidence of any phase transformation up to a pressure of 15 GPa. Pmn2(1)-Li(2)MnSiO(4) shows an unusual expansion of the a lattice parameter upon compression. A density functional theory investigation yields lattice parameter variations and bulk moduli in good agreement with experiments. The calculated data indicate that expansion of the a lattice parameter is inherent to the crystal structure and independent of the nature of the transition-metal atom (M). The absence of pressure-driven phase transformation is likely associated with the incapability of the Li(2)MSiO(4) composition to adopt denser structures while avoiding large electrostatic repulsions.

Unfolding Action of Alcohols on a Highly Negatively Charged State of Cytochrome c

It is well-known that hydrophobic effect play a major role in alcohol-protein interactions leading to structure unfolding. Studies with extremely alkaline cytochrome c (U(B) state, pH 13) in the presence of the first four alkyl alcohols suggests that the hydrophobic effect persistently overrides even though the protein carries a net charge of -17 under these conditions. Equilibrium unfolding of the U(B) state is accompanied by an unusual expansion of the chain involving an intermediate, I(alc), from which water is preferentially excluded, the extent of water exclusion being greater with the hydrocarbon content of the alcohol. The mobility and environmental averaging of side chains in the I(alc) state are generally constrained relative to those in the U(B) state. A few nuclear magnetic resonance-detected tertiary interactions are also found in the I(alc) state. The fact that the I(alc) state populates at low concentrations of methanol and ethanol and the fact that the extent of chain expansion in this state approaches that of the U(B) state indicate a definite influence of electrostatic repulsion severed by the low dielectric of the water/alcohol mixture. Interestingly, the U(B) ⇌ I(alc) segment of the U(B) ⇌ I(alc) ⇌ U equilibrium, where U is the unfolded state, accounts for roughly 85% of the total number of water molecules preferentially excluded in unfolding. Stopped-flow refolding results report on a submillisecond hydrophobic collapse during which almost the entire buried surface area associated with the U(B) state is recovered, suggesting the overwhelming influence of hydrophobic interaction over electrostatic repulsions.

Expansion of the pentafluorobenzene ring and other skeletal transformations in the reaction of perfluoro(1,2-diethyl-1-phenyl-1,2-dihydrocyclobutabenzene) with antimony pentafluoride

The reaction of perfluoro(1-phenyl-1,2-diethyl-1,2-dihydrocuclobutabenzene) with SbF5 at 20°C, followed by treatment of the reaction mixture with water gave perfluoro {4-[1-(2-propylphenyl)propylidene]-2,5-cyclohexadien-1-one} together with perfluoro[4b,10-diethylbenzo[a]azulen-7(4bH)-one] resulting from unusual expansion of the pentafluorobenzene ring to seven-membered ring. Analogous reaction at 90°C, apart from the above compounds, afforded perfluorinated 10-ethyl- and 3,10-diethylbenzo[a]azulen-6(10H)-ones via elimination of C2F5 group from the seven-membered ring or its migration to the benzene ring.

The Thermal Expansion, Elastic and Fracture Properties of Porous Cordierite at Elevated Temperatures

The properties that determine the thermal shock resistance in materials are reported for porous cordierite, a leading candidate material for the fabrication of diesel particulate filters. Fracture toughness and slow crack growth tests were performed on test specimens obtained from the walls of diesel particulate filter monolithic substrates using the double‐torsion test method at temperatures between 20°C and 900°C. The thermal expansion and elastic properties were characterized between 20°C and 1000°C. The role of the microstructure of porous cordierite in determining its unusual thermal expansion and elevated temperature Young's modulus and fracture toughness are discussed.

Exceptional negative thermal expansion and viscoelastic properties of graphene oxide paper

We report unusual negative thermal expansion and viscoelastic properties in graphene oxide paper. The paper was prepared from aqueous GO dispersions using a simple vacuum evaporation technique. From room temperature to 150°C, this paper-like graphene oxide sheet exhibits a constant negative thermal expansion coefficient of −67×10−6/°C along the in-plane direction. Peculiar hysteresis loops of thermal expansion-temperature curves are observed, which are affected by the cooling rate and starting temperature of cooling. The tensile tests on GO paper show clear hysteresis loops, revealing the viscoelastic property of the paper. The viscoelastic properties show excellent frequency-stability in the range of 1.0–60Hz. In the low temperature range −150 to 25°C, however, they show a strong temperature dependence. The storage modulus of the graphene oxide paper continuously increases with decreasing temperature.

A small molecule regulates hairpin structures in d(CGG) trinucleotide repeats

Unusual expansion of trinucleotide repeats has been identified as a common mechanism of hereditary neurodegenerative diseases. Although the actual mechanism of repeat expansion remains uncertain, trinucleotide repeat instability may be related to the increased stability of an alternative DNA hairpin structure formed in the repeat sequences. Here we report that a synthetic ligand naphthyridine carbamate dimer (NCD) selectively bound to and stabilized an intra-stranded hairpin structure in CGG repeat sequences. The NCD–CGG hairpin complex was a stable structure that efficiently interfered with DNA replication by Taq DNA polymerase. Considering the sequence preference of NCD, the use of NCD would be valuable to investigate the genetic instabilities of CGG/CCG repeat sequences in human genomes.

Magnetization, Mössbauer and isothermal dilatometric behavior of oxidized YBa(Co,Fe)4O7+δ

Mössbauer spectroscopy and magnetization studies of YBaCo(4-x)Fe(x)O(7+δ) (x = 0-0.8) oxidized at 0.21 and 100 atm O(2), indicate an increasing role of penta-coordinated Co(3+) states when the oxygen content approaches 8-8.5 atoms per formula unit. Strong magnetic correlations are observed in YBaCo(4-x)Fe(x)O(8.5) from 2 K up to 55-70 K, whilst the average magnetic moment of Co(3+) is lower than that for δ ≤ 0.2, in correlation with the lower (57)Fe(3+) isomer shifts determined from Mössbauer spectra. The hypothesis on dominant five-fold coordination of cobalt cations was validated by molecular dynamics modeling of YBaCo(4)O(8.5). The iron solubility limit in YBaCo(4-x)Fe(x)O(7+δ) corresponds to approximately x ≈ 0.7. The oxygen intercalation processes in YBaCo(4)O(7+δ) at 470-700 K, analyzed by X-ray diffraction, thermogravimetry and controlled-atmosphere dilatometry, lead to unusual volume expansion opposing to the cobalt cation radius variations. This behavior is associated with increasing cobalt coordination numbers and with rising local distortions and disorder in the crystal lattice on oxidation, predicted by the computer simulations. When the oxygen partial pressure increases from 4 × 10(-5) to 1 atm, the linear strain in YBaCo(4)O(7+δ) ceramics at 598 K is as high as 0.33%.

On the high-temperature phase of barbituric acid

The crystal structure of the high-temperature phase (HT-form or form III) of barbituric acid has been solved from X-ray powder diffraction data. It was found to be monoclinic, space group C2/c, a = 8.5302(3) A, b = 6.8167(3) A, c = 9.3304(4) A, β = 89.865(2)°, volume = 542.54(4) A3 at T = 236(1) °C. The crystal structure is closely related to the also monoclinic structure of form II. A combined Rietveld refinement of X-ray and neutron powder diffraction data revealed fine details of the disorder aspects of the structure. 1H variable temperature and 13C MAS solid-state NMR confirmed those and proved the dynamic nature of the rotational disorder of the molecules. Energy optimizations of ordered subgroup structures with dispersion-corrected DFT gave insights into the underlying reason for the disorder. The reorientation of the unique 2-fold symmetry axis at the II → HT phase transition derives from both the anisotropy of the hydrogen bonds and the resulting anisotropy of the thermal rotational disorder. The unusual thermal expansion behavior of form II also finds its explanation in the incipient disorder.

On the liquid-state fragility of PdNiCuP metallic glasses

It has been widely known that Pd–Ni–Cu–P alloy system possesses the largest glass forming ability among the bulk metallic glasses. But its fragility exhibits relatively low index, lower than other good metallic glass formers. Intensive research has been done on glass forming ability, and it has been suggested that the sluggish diffusive motion and small driving force for nucleation are responsible for this unusual phenomena. However, this apparent contradiction between glass forming ability and fragility is not unique among vitreous materials. Considering the same details of vitrification of water and thermodynamic fragility, as well as unusual expansion during solidification of PdNiCuP metallic glass, it is suggested tentatively that there might be a fragile-to-strong transition during the vitrification of PdNiCuP metallic glass.